Tumors and lesions are pathological anatomies characterized by abnormal growth of tissue resulting from a progressive, uncontrolled multiplication of cells, while serving no physiological function. Pathological anatomies can be treated with invasive procedures, such as surgery, but these procedures can be risky and/or harmful for the patient.
A non-invasive method to treat a pathological anatomy (e.g., tumor, lesion, vascular malformation, nerve disorder, etc.) is external beam radiation therapy. In one type of external beam radiation therapy, an external radiation source is used to direct a sequence of x-ray beams at a tumor site from multiple angles. As the angle of the radiation source changes, each beam passes through the tumor site, but travels through a different area of healthy tissue on its way to the tumor. Ideally, the cumulative radiation dose at the tumor is high and the radiation dose to healthy tissue is low.
Radiation therapy typically includes a planning phase in which locations for the radiation beams are determined, and a treatment phase in which the radiation beams are administered. During the planning phase, a software package may be used to import three-dimensional (3-D) images, such as computerized x-ray tomography (CT) scans, for delineating structures to be targeted or avoided during treatment. A goal of the planning phase is to identify a dose distribution (i.e., a collection of radiation beams) that conforms to the tumor, while avoiding critical structures or organs at risk, such as the spinal cord or healthy brain tissue.
During the treatment phase and just prior to the administration of radiation, 3-D images may again be collected to determine whether the tumor has undergone morphological changes and/or moved with respect to nearby critical structures. To account for any changes that have occurred, the dose distribution identified during the planning phase may need to be moved, adjusted, and/or completely reworked. For example, with one approach, the proposed dose distribution is moved until it falls outside of exclusion zones placed around the critical structures. With another approach, the shape of the dose distribution is changed (e.g., by adjusting the shapes and/or relative positions of the radiation beams) until the dose distribution does not contact or intersect critical structures. Unfortunately, adjusting the proposed dose distribution can be a time consuming and expensive process.
Accordingly, a need exists for methods and systems that allow a proposed dose distribution, identified during the planning phase, to be utilized during the treatment phase with a minimal amount of adjustment, despite morphological changes and/or movements that may have occurred between a tumor and one or more critical structures.